Due to short of energy, enhancement of the public environmental awareness, and increasingly strict regulations of the government, environment friendly electrical vehicle and fuel cell vehicle emerge. However, due to various constraints on the technology, vehicles of such types are difficult to be comprehensively popularized in a short time. Therefore, a hybrid electrical vehicle which has been relatively mature in technology is a comparatively desired choice at present.
As a new type of energy saving, environment friendly vehicles, hybrid electrical vehicles (HEV) are in a booming phase in terms of technology and market. The biggest difference of hybrid electrical vehicles from conventional internal combustion engine vehicles and pure electric vehicles is the powertrain.
In parallel configuration and hybrid configuration of HEV, power coupling systems combine multiple powers of the HEV together, realizing a reasonable power distribution among the multiple power sources and transmitting the powers to the drive axles. Thus, power coupling systems play an important role in the development of HEV, their performances being directly related to whether the HEV overall performances reach design requirements or not, and are the most key part of HEV.
Planet gear sets are characterized with multiple freedoms and flexible controllability of input/output, and are of a compact structure, a small volume and a big range of speed ratios, thus are employed in more and more power coupling systems of hybrid electrical vehicles, this is also a development tendency of power assemblies of hybrid electrical vehicles nowadays.
Toyota proposed the first hybrid electrical vehicle Prius in 1997, and further proposed Prius 2006 carrying the most new 3rd generation of electromechanical hybrid powertrain, still utilizing the hybrid powertrain THS of a hybrid configuration, wherein a planet gear system redistribute the output power from the engine, realizing a purpose of reasonably balancing the loads of engine.
FIG. 1 shows a structure principle diagram of the powertrain for the Toyota Prius hybrid electrical car. The powertrain thereof comprises an engine E, a motor MG1, a motor MG2 and a power coupling system comprising a planet gear set of one single planet gear rank, and etc. In this powertrain, engine E connects to a planet carrier a of the planet gear set of one single planet gear rank through a shock absorbing damper, and transmits the power to an outer ring gear c and a sun gear d via a planet gear b. the outer ring gear c is connected to a output shaft, the output shaft connects to the rotor of the motor MG2 through a reducing gear set e. The sun gear d connects to the rotor of the motor MG1. The output shaft transmits the power to the wheels through a chain drive system f, a main reducer g and a differential h. The system transmits most of the torque of the engine E directly to the output shaft, and transmits a small part of the torque to the motor MG1 for electricity generation, the electricity energy generated by the motor MG1 is used for battery charging, or driving the motor MG2 to increase the drive force according to instructions. This structure may enable the engine in an efficient region or a low emission region all the time by adjusting the torque and the rotational speed of the motor MG1. Furthermore, through adjusting the rotational speeds of various elements of the planet gear set, it can work in a similar manner to a continuously variable transmission.
However, as the two motors MG1, MG2 of the above said powertrain are arranged on both sides of the planet gear set of one single planet gear rank, and share a set of cooling system, the arrangement of the motor cooling system is complex, the integrated level of the motor system is low, and the drive shafts on the both sides of the planet gear set are not equal in length, not facilitating the arrangement of a nose cabin. Moreover, motor MG1 and engine E are parallel arranged on the same side of the planet gear set, as the distance therebetween is short, and the optimal operation temperature of the motor MG1 is 60 centigrade degree, but the optimal operation temperature of the engine E is 90 centigrade degree, motor MG1 may heat quickly under the influence of the heat dissipation from the engine E, making the corresponding motor cooling system often be in a high load operation condition, in turn affecting the efficiency of the overall vehicle.
As abovementioned powertrains employ a planet gear set of one single planet gear rank, its reduction ratio range is small, and thus a wide variation range of the rotational speed of the motor is required, high requiring the torque of the motor. Therefore, the requirements on the manufacture accuracy, rotational speed/torque characteristics and dynamic balance of the motor are very harsh. In order to achieve adequate reduction ratio, the reduction device for the output shaft employ multi-stage drive components including the chain drive system f, the main reducer g, further increasing the complexity of the system, and enhancing the requirements of the system on the space arrangement.
China patent document CN 101149094A discloses a hybrid drive device based on a planet gear system of two planet gear ranks, comprising an internal combustion engine, a motor, and an power output and front and rear planet gear ranks. Wherein the planet carrier of the front planet gear set is connected to the ring gear of the rear planet gear set, the sun gears of both front and rear planet gear set are commonly connected to the motor shaft, the engine is selectively connected to the ring gear or planet carrier of the front planet gear set through a clutch, the planet carrier of the rear planet gear set is connected to the output. As its front and rear planet gear set are parallel arranged, it has relatively large shape dimensions, and the structure is not compact enough; for only two input shaft and one motor exist, requirements on the controlling of the motor are high.
Therefore, in the art, there exists a need for improving the powertrain of hybrid electrical vehicles, in particular the power sources coupling structure or drive device thereof.